Light Detection and Ranging (LIDAR) is a well-established process for remote sensing and imaging. Commercial systems are widely employed for airborne terrain mapping providing the most accurate topographic data available. Recently, LIDAR technology has been extended to the point where high resolution 3-D imagery can be obtained for the detection and identification of targets. Certain LIDAR configurations provide the ability to range-gate, that is isolate precise range intervals using pulsed lasers and gated detectors. Range-gated LIDAR has been shown to be able to detect and ID partially hidden targets through obscurations such as foliage and smoke. However, current methods requires unacceptably long collection times, as well as small-area (<32×32 pixels), expensive, custom focal planes.
By definition, imaging through an obscuration implies that much of the light is lost in transmission to and from the target. Because of this, complex detection systems and high-powered laser sources are currently required, and to date have offered limited capabilities. For instance, imaging sensors known as Geiger-mode Avalanche Photodiode Arrays (GM-APDs) have been developed over the last several years to provide the sensitivity and timing information required. These are small two-dimensional arrays of detector elements capable of measuring single-photon events and recording their associated time-of-arrival to provide the needed range information to generate a 3-D image. GM-APDs are typically low spatial resolution devices that can be difficult to fabricate, and require long sampling times to accumulate adequate signal-to-noise. State-of-the-art sensors in the short wave IR (SWIR) region (1.2-1.9 microns) typically only provide 32×32 pixel resolution. While R&D continues to improve resolution, signal-to-noise, and timing accuracy, the number of photons available to be detected continues to be the dominant limiting factor.
Conventional LIDAR systems can obtain 3-D imagery of objects of interest, or targets, even when significantly obscured, such as by a tree canopy. However, the returned image from the target is limited and can greatly affect search rates, signal-to-noise, integrations time, and can be quite noisy due to the paucity of returning photons. Therefore, to acquire a usable image in conventional LIDAR systems one must often integrate for a long time, perform multiple passes, reduce the standoff range, and/or resort to prohibitively large and more powerful laser illuminators
Accordingly, a need remains in the art to develop a system and method of increasing the amount of light actually striking an obscured target and bypassing and/or reversing the effects of the obscurations by utilizing an optical phase conjugation process.